/Engine/Source/Runtime/Core/Public/Misc/CString.h
Helper function to write formatted output using an argument list
number of characters written or -1 if truncated
static int32 GetVarArgs ( [CharType](API\Runtime\Core\Misc\TCString\CharType) * Dest, SIZE_T DestSize, const [CharType](API\Runtime\Core\Misc\TCString\CharType) *& Fmt, va_list ArgPtr )